It is advantageous in access performance to perform the recording and reproducing of an optical disk such as a DVD and a CD by CAV (Constant Angular Velocity), and therefore, the recording and reproducing by CAV is generally used. However, in this case, a transfer rate of a data reproduced from a disk and a recording rate of a data recorded to the disk change in a range of about 2.5 times. According to this, Jyh-Shin Pan et al., “Fully Integrated CMOS SoC for 56/18/16 CD/DVD-dual/RAM Applications with On-Chip 4-LVDS Channel WSG and 1.5 Gb/s SATA PHY”, ISSCC 2006 DIGEST TECHNICAL PAPERS, pp. 266-268 (Non-Patent Document 1) describes a promotion of the power saving by changing a frequency of a clock supplied to units for an error correction, a modulation, a demodulation, and the like.
Also, Japanese Patent Application Laid-Open Publication No. 2003-91942 (Patent Document 1) describes that, in a signal process for reproducing a DVD, a trigger signal is issued each time one ECC block (ECC: Error Correcting Code) is reproduced from a disk, and a frequency of a clock supplied to units for an error correction, a demodulation, and the like changes depending on either the ECC process already ended or not when the trigger is generated.
Further, Japanese Patent Application Laid-Open Publication No. H11-232039 (Patent Document 2) describes that, in a signal process for reproducing a DVD, the signal processing is performed without a crash by setting an error correcting process time so as to match an end time of an access of an error correcting process circuit from/to a memory even if data accesses of a demodulating circuit and an output circuit from/to the memory is temporally increased.